Obesity is a major public health problem. Behavioral weight loss programs have been shown to be successful in reducing body weight and preventing the onset of medical complications of obesity. There is a need to develop cost-effective approaches to disseminating these weight loss interventions. This project evaluates an innovative approach to disseminating weight loss interventions. It uses a self-sustaining statewide program called Shape Up Rhode Island, as a means of recruiting large numbers of participants to the program and combines this program with effective behavioral weight control strategies to improve the weight loss outcome. Shape-Up Rhode Island is a 12 week program to help Rhode Islanders lose weight and increase activity through an Internet delivered team-based competition, which recruited over 13,000 participants in 2009. To avoid markedly increasing personnel costs or participant burden, the Shape-Up Rhode Island program will be enhanced with a behavioral weight loss intervention including (1) education about diet, exercise and behavior strategies delivered via weekly multi-media behavioral lessons based on the Diabetes Prevention Program and Look AHEAD, that can be viewed by the participant on their computer; and (2) increased accountability through submission of weekly self-monitoring records and computer-generated individualized feedback. A pilot study of this enhanced intervention indicated that participants in Shape-Up RI adhered well to these added components and that the enhanced program significantly improved weight losses in the Shape-Up RI program. We propose to conduct a randomized controlled trial with 600 Shape-Up Rhode Island participants who will be randomly assigned to receive the 12-week standard Shape-Up Rhode Island program or an enhanced program, which includes not only the standard Shape-Up Rhode Island program, but also weekly video behavioral lessons and weekly automated feedback. The primary hypothesis is that the enhanced program will improve weight losses at week 12. Secondary aims are to compare the treatments on percent of participants achieving a 5% weight loss, on 6 and 12-month follow-up, and on behavior changes related to weight control, and to conduct cost-effective and cost-utility analyses comparing the two programs. This innovative intervention, which uses a statewide campaign for outreach combined with effective behavioral strategies for weight loss success, has the potential to be an important public health model for the treatment of obesity.